Handheld Large 2-D Array With Azimuthal Planewave and Row-Multiplexed Elevation Beamforming Enabled by Local ASIC Electronics.

Large-aperture 2-D arrays benefit from improved lateral resolution at depth, due to the dependence of beamwidth on the inverse of the aperture width, and improved contrast resolution due to electronic focusing. We have been developing modular large-aperture multirow 1024 (64 azimuth $\times 16$ elevation) element, 2-D arrays based on custom-designed and locally integrated application-specific integrated circuit (ASIC) multiplexing devices. The implemented handheld large-array prototype probe for human imaging consists of multiple rows with multiplexed synthetic aperture in elevation and planewave transmits in azimuth. The pitch of the acoustic array is $650~\mu $ m in azimuth by $1000~\mu $ m in elevation, with a 2.4 MHz fractional bandwidth (FBW =88%) center frequency and total active aperture of $42\times 16$ mm. We interfaced the large aperture array and multiplexing ASICs, along with local preamplifier devices for improved sensitivity, and a local FPGA for digital ASIC control, to a configurable ultrasound imaging platform and demonstrate 2-D orthogonal and full 3D beamformed imaging. The implemented imaging prototype includes local buffering for improved sensitivity of the high-impedance 2-D array elements, and realizes penetration down to 140 mm, experimental lateral/axial resolution at 67 mm of 1.1/0.4 mm, and maximum experimental CNR of 2.1 for 8 mm cylindrical cysts and 1.7 for 10 mm spherical cysts. We demonstrate in vivo imaging of liver in human volunteers utilizing a hermetically sealed and safety-validated handheld prototype of the large 2-D array. Preliminary results are promising for clinical imaging in future studies.